Two-stroke revival - Will TM keep them alive?

[jlv]

The displacement rule isn't new as far as I know. Four strokes have just advanced enough to where they are more than half as powerful at the same size now.

[Wilmx829]

Why don't they put that much technology and research into two strokes?

[Phathry25]

Why don't they put that much technology and research into two strokes?

It's a conspiracy.

[Voutare]

Why don't they put that much technology and research into two strokes?

Because 4 strokes are the future of MX. As much as you want to keep your 2t, eventually, 4 strokes are going to be dominant. It's progression. The factories know what is best for us, no matter if we realize it or not.

It's like Social Security for us Americans. At first we were screaming communism and socialism, and now its the most important part of you, and no one hates it.

[Axle McOctane]

Why don't they put that much technology and research into two strokes?

Because 4 strokes are the future of MX. As much as you want to keep your 2t, eventually, 4 strokes are going to be dominant. It's progression. The factories know what is best for us, no matter if we realize it or not.

It's like Social Security for us Americans. At first we were screaming communism and socialism, and now its the most important part of you, and no one hates it.

I really hope you're kidding. In fact, I am absolutely F_ _ _ing terrified and astonished at the level of Orwellian brainwashing just expressed.

And electric bikes are the future of MX. Actually there are propulsion systems lightyears ahead of internal combustion engines.

[Wilmx829]

F all that, 2stroke or die trying.

[Voutare]

Not to mention 4 strokes are a lot more eco friendly. (Or at least people say they are.), so that'll keep the environmentalists at bay a bit more.

[jbob23]

Not to mention 4 strokes are a lot more eco friendly. (Or at least people say they are.), so that'll keep the environmentalists at bay a bit more.

the new 2 strokes supposedly in the works are cleaner and more efficient than 4 strokes. somehow...... lol

[JETZcorp]

They do it by eliminating the old problem. With the "old" two strokes (like my 250 and all the bikes made today) you had air, gas, and oil being pumped from the crankcase into the cylinder, while the exhaust was being pushed out at the same time. This meant that some of the air, gas, and oil just shot out the exhaust without getting a chance to be burned. With fuel injection, only air (and maybe oil depending on the approach) has to deal with this problem, and gas is injected after the exhaust is sealed by the piston. But, because the two-stroke doesn't have that extra stroke causing heat and friction, and because it's not using its power to run valves, it burns less gas than a same-displacement four-stroke. And, if you want to cling to that double-displacement rule, the advantage becomes rather gigantic. Outboard motors are marketed by horsepower and not by displacement, the two-strokes like E-Tec and Opti-Max can claim a huge benefit at the pump because they're getting the same power on less displacement. And, because they don't even have to worry about transfer ports and use a supercharger instead, they have become known for their broad and usable powerband.

http://www.youtube.com/watch?v=_-7I00cZUE0
^^ Some question whether Evinrude are being honest in this test. Who knows.

Why don't they put that much technology and research into two strokes?

They want four-strokes to be dominant in the sport, as Voutare noted. When someone needs to re-build their two-stroke, it's a fairly cheap affair. Even with proper maintenance, all bikes break down and need to be rebuilt. When you need to re-build your four-stroke, they make a lot more money in parts because valves become part of the equation too. Even if they're both equally reliable, they can still make more profit on the fours. A company like Suzuki, which also makes cars, is likely to want to simplify operation and cut expenses by sharing technology. If their dirt-bike guys come up with a hot idea, it can go into next year's Grand Vitara, and vice versa. If they were making two-stroke dirt-bikes, they wouldn't be able to share the engine technology (unless they made two-stroke cars.)

The displacement rule isn't new as far as I know. Four strokes have just advanced enough to where they are more than half as powerful at the same size now.

It depends on your definition of "new." I believe it started with the YZ400F in the late '90s. Before then, if you wanted to race a 500cc four-stroke, you had to do it against a 500cc two-stroke. Even Honda, who were able to say, "Honda views itself as a four-stroke company that will not be satisfied until it wins all of its championships with four-strokes" in 1984, were forced to use two-strokes in motocross and road racing because it was just that much better when you put them on an equal footing. It was like steam being replaced with diesel in railroads. As soon as the four-strokes were given legislative training wheels and allowed to be bigger (by this time the 500cc two-strokes were out the door, even though it was the most popular class in amateur racing) and the bike makers put all their money into the four-strokes. None of the Big 4 put anything into their two-stroke engines in the last five years or more, and Honda have now gone as far as to get rid of even the two-stroke mini-bikes in their line-up. Company policy, right?

One can't deny that they've done a lot with the money they've invested. The four-strokes have progressed immensely since the YZ400F and are now quite advanced. In fact, the new YZ250F is a few pounds lighter than the two-stroke YZ250, thanks to all the development. It's said a 250F can get faster lap times than a 250 2T if the track has bad grip, and the advantage shifts from hour to hour. Sometimes, the pure power of a 2T gives the advantage and sometimes the tame mildness of a 4T gives the advantage. But it's pretty clear that nothing gives the 4T an advantage quite as much as being allowed to legally cheat. If someone wants to say that 250 vs 250 isn't fair... well, think about it. There's no replacement for displacement.

[jlv]

I could have swore the old rules said four strokes get twice the displacement, but I just checked and you're right. It says 125, 250 etc. with no four stoke exception.

[Phathry25]

It's said a 250F can get faster lap times than a 250 2T if the track has bad grip, and the advantage shifts from hour to hour.

Where was that said? In the TWMX Article w/ JLaw? And anyways, what self respecting track/promoter is going to allow it's track to get that bad that the 250f can make up 3-4 seconds a lap just because it has smoother and less power?

There's no replacement for displacement.

You're comparing apples to oranges with that quote. If you compare engine efficiency you'll see that the 4T is considerable more efficient at producing power. For every 250cc's of air flowing through a 4T engine there is 500cc's or air going through a 250cc 2T engine. So in essence they have the same displacement. Am I right?

[jlv]

I doubt a two stroke will move 2x the amount of air that an equal displacement four stroke will. Also, the compression stoke for a two stroke starts at the top of the exhaust port (although the pipe helps that a little). So it isn't getting the as much power per power stroke as an equal displacement four stroke. None of this matters for making rules though. It's whatever the racing organization wants. IIRC the AMA made all kinds of rules to keep Harley competitive in flat track.

I can see how people like four strokes since they are nice easy to ride bikes, but it's hard to argue that a motor that has a much worse power to weight ratio is superior. If you set out to make the best motorcycle under 200 lbs, you would choose a two stroke motor since it's more powerful for the same weight. If you set out to make the best 40 hp bike, you would also go with a two stroke since a 40 hp two stroke motor is much lighter than a 40 hp four stroke.

[Phathry25]

IIRC the AMA made all kinds of rules to keep Harley competitive in flat track.

This is an outrage!!! I'm sure the AMA's lawyers will be sending you a cease and desist soon. LOL.

[jlv]

Don't laugh! If Harley tries to get into MX we'll all be riding 900cc flatheads!

[Phathry25]

LOL. Harley just shut down Buell, I don't think they have the money to make rules right now. FINALLY!!!!!!!